Agomelatine is an antidepressant drug having the following formula (I)

Agomelatine has been described and claimed in the patent EP0447285. In said document, agomelatine is obtained by reaction between 2-(7-methoxynaphth-1-yl)-ethylamine and acetyl chloride and classic recrystallization from isopropyl ether. The agomelatine thus obtained has a melting point of 109-110° C.; no information is provided on the type of crystalline form of the molecule.
Acta Cryst., 1994, C50, 907-910, reports for the first time a crystallographic analysis of agomelatine.
EP1564202 claims a form defined as “form II” which is obtained by reaction between 2-(7-methoxynaphth-1-yl)-ethylamine and sodium acetate and acetic anhydride in ethanol and washing of the precipitate with a water/ethanol mixture.
Said crystalline form has a melting point of 108° C. and presents specific crystallographic characteristics.
A series of successive patents describe further crystalline forms of agomelatine, in particular forms III to VI, prepared according to particular methods (crushing, atomization, crystallization in particular solvents, etc.).
EP2319827 describes a process for the preparation of crystalline form I of agomelatine which entails dissolving the agomelatine in an organic solvent miscible with water and pouring the solution thus obtained into water having a temperature equal to or below 30° C.
Also CN101704763A describes a process for the preparation of form I of agomelatine which is very similar to that of EP2319827, at a temperature of between 0° C. and 100° C.
However, the processes described in EP2319827 and CN101704763A have some drawbacks. The applicant has tried to repeat said processes and has observed that they are not reproducible with constant results, because they produce different crystalline forms and often mixtures of different crystalline forms of agomelatine.